feat: add user display profiles and fix web context menu UX

backend:

- add required user name and optional bio fields

- extend auth/register and user schemas/services with name/bio

- add alembic migration 0006 with safe backfill name=username

- compute per-user chat display_title for private chats

- keep Saved Messages delete-for-all protections

web:

- registration now includes name

- add profile edit modal (name/username/bio/avatar url)

- show private chat names via display_title

- fix context menus to open near cursor with viewport clamping

- stabilize +/close floating button to remove visual jump

app/users/repository.py

@@ -4,8 +4,8 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.users.models import User
 
 
-async def create_user(db: AsyncSession, *, email: str, username: str, password_hash: str) -> User:
-    user = User(email=email, username=username, password_hash=password_hash, email_verified=False)
+async def create_user(db: AsyncSession, *, email: str, name: str, username: str, password_hash: str) -> User:
+    user = User(email=email, name=name, username=username, password_hash=password_hash, email_verified=False)
     db.add(user)
     await db.flush()
     return user